Tohti's family has received no news of him since his arrest at his Beijing home on 15 January. No one knows for sure, but he may have been secretly transferred to a prison in the Xinjiang Uyghur Autonomous Region.

"The public security bureau in Urumqi, the capital of Xinjiang, has reported online that Ilham Tohti is accused of inciting separatism but no police station has been able to tell his family where he is being held," said Benjamin Ismaïl, the head of the Reporters Without Borders Asia-Pacific desk.

"We deplore the use of methods that are illegal under both Chinese law and international standards. We call on the authorities to reveal where they are holding Tohti and to allow his lawyer and his family to visit him."

According to a report posted online on 25 January, the authorities accuse Tohti of heading a separatist group that advocates the use of violence to overthrow the Chinese government in Xinjiang and of using his Uygurbiz.com website to recruit followers.

The authorities also claim to suspect him of links with the Eastern Turkistan Islamic Movement, which wants an Islamic state in "Eastern Turkistan" (Xinjiang) and which the Chinese government regards as terrorist organization responsible for acts of violence.

To help Tohti, Reporters Without Borders urges everyone to put pressure on authorities to reveal his location by calling as many police stations in Beijing and Urumqi as possible and asking:

A teacher at Beijing's Central University for Nationalities, Tohti is a well-known government critic and opponent of the regime's repressive policies in Xinjiang and, as result, has long been under permanent state security surveillance. He was held incommunicado for more than a month in 2009 after relaying information about rioting in Xinjiang.

China is ranked 173rd out of 179 countries in the 2013 Reporters Without Borders press freedom index.

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